It is possible that the main title of the report Marfan Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
As Jenny points out, being able to lisp the alphabet song at age two has little to do with 'knowing' the alphabet. And, yes, most children learn the letters by sight and sound in kindergarten, although most are capable of learning this information sooner if diligently taught by parents or others.
At the start of this period, most kids can follow directions and say 50 or more words. Many combine words in short phrases and sentences. By age 3, a toddler's vocabulary usually is 200 or more words, and many kids can string together three- or four-word sentences. Kids at this stage of language development can understand more and speak more clearly. By now, you should be able to understand about 75% of what your toddler says.